Ever since automobiles became popular, disposal of their discarded pneumatic tires (referred to as "casings") has been a never-ending source of problems. The problems have been exacerbated by the exponential growth of the automobile industry and the commercial adoption of the steel-belted radial tire. The term "casing" is used hereinafter to refer specifically to a worn out tire. It will be appreciated that, except in those instances where a tire manufacturer must dispose of unused scrap tires, this invention will deal with radial ply casings. In particular, it will concern chiefly the steel-belted portion (for reasons which will be set forth hereunder) of the annular crown of the casing, after it has been cut open to form a flat strip, and the tread has been sliced off the crown. The cut is made along the longitudinal axis of the annular crown.
A steel-belted radial passenger tire is conventionally constructed with a pair of tread reinforcing rubber belts or plies, one placed radially inwardly of the other, the plies having cords with equal and opposite cord angles relative to the midcircumferential center plane of the tire. The cords in each belt are in parallel spaced apart relationship. When bonded together by vulcanization in a curing press, the two plies form a laminate which reinforces the tread, the mechanical properties of the cured laminate being greatly different from those of the uncured belts, because of the constraint dictated by the cord geometries and interply bonding. The cords in the reinforcing belt are desirably made of a high modulus relatively inextensible material, such as steel, glass, aramid or rayon. At present, steel belts are preponderantly used, and it is to steel-belted radial tires to which this invention is chiefly directed, though it will be evident that belts of other essentially inextensible reinforcing cords may also be used.
Once the tire is cured, the cured laminate of two plies behaves as a unitary article encasing the carcass ply or plies, and since this invention is mainly directed to the surprisingly simple use of the belted portion of a casing, shorn of its remaining tread, this belted portion including the carcass ply or plies, will be referred to hereinafter as the "belt", and the individual components of the "belt" will be referred to as "belt plies", for the sake of convenience. All references to a "belt" will be to a belted portion of the crown, irrespective of the material of the reinforcing cords, and includes the carcass ply or plies, and the tubeless tire liner, if present, but without the tread, except as otherwise stated. Typically, a steel-belted passenger tire will have a belt with two belt plies, one next to the tread, referred to as the "outer" ply; and one next to the carcass plies, referred to as the "inner" ply, without regard to the location of the belt in a particular configuration of laminate.
Tires, particularly if piled high to store them on open ground, provide good breeding places for encephalitis-bearing mosquitos and an excellent refuge for vermin. Tires are flammable. Fires fed with tires produce a sooty flame and malodorous, if not toxic, vapors. The oily pyrolysate generated contaminates ground waters. Therefore such storage of tires is objectionable.
The formerly widespread practice of burying whole tirres in landfills is also objectionable because the landfill is too unstable for building construction. Buried tires entrain air and tend to float to the surface. To avoid this latter problem, casings may be sliced in half, or chopped into coarse pieces. To do so is costly and of course generates no positive value.
In any consideration of the problems of recycling scrap tires, rather than incinerating them, it will generally be agreed that the best thing to do with a worn out tire is to retread it. In practice, presently about 10 percent of the tires worn out annually are retreaded. All other recycling requires first chopping up the tires into smaller pieces, even if the only intended use is for landfill.
Unfortunately, it is difficult and uneconomical to chop up the belt portion of steel-belted radial tires. This fact has deterred to a considerable extent the development of practical, commercially significant processes to recycle worn out casings into useful articles.
Therefore, much effort has been directed to the aspects of resource conservation, namely reclaiming; and of energy conservation, namely utilization for generating energy.
Resource conservation by chemical processing reclamation, by pyrolysis, whether by microwave energy or thermal pyrolysis, or reclamation by cryogenically or mechanically comminuting the sliced off rubber tread and sidewalls, are all significant, but economically still onerous. Reclaimed rubber has properties inferior to virgin rubber, the end products from pyrolysis do not command a high enough price in the marketplace for pyrolysis to be economically attractive at the present time, and the markets for ground scrap rubber are constricted.
Energy conservation by incineration of casings, sometimes whole, but more often, appropriately chopped up, has come to the forefront as a solution to the disposal problem, provided of course, such burning is done in an environmentally acceptable manner.
A large number of references deal with the foregoing aspects of the problem, among which is a series of articles by T. Ohkita, et al under the title "Effective Utilization of Utilising Scrap Tires" in Parts (I), (II) and (III) dealing respectively with "High temperature tensile tests on vulcanised rubbers"; "Reclamation of rubber from waste passenger tyres under various conditions and high temperatures"; and, "Mixing of asphalt and reclaimed rubber from waste passenger-car tires". Like others in the field, they use chemically reclaimed rubber or mechanically ground rubber particles in blends which are vulcanized. To my knowledge no one has suggested vulcanizing or otherwise bonding the "belt" of one casing with another to take advantage of the unexpected physical properties of such a laminate.
Specialty products provide a limited use of casings. For example, portions of casings of non-radial tires, sometimes with fabric belts (but without steel belts) have been reused by cutting out the beads and sidewalls, and planing away the remaining tread rubber to leave a flat strip of fabric-reinforced vulcanizate. From this fabric-reinforced strip, smaller pieces of chosen size and shape are `died out` (cut) for use as muffler and tail-pipe hangers on new automobiles, inter alia. A steel-belted portion from the crown of a tire is unsuitable for such processing because of the present technical inability to die cut the belts economically.
Another very limited use of casings is to form crash barriers on highways, breakwaters, and artifical reefs to enhance growth conditions for marine and fish life in the ocean. This latter use is limited to regions where the weather is warm enough to form reefs, even if the high cost of ferrying casings to an appropriate site is disregarded.
The problem of how to cut up steel belted portions of a casing remains. The better solution is to cut up and use those portions of the tires which lend themselves to doing so, yet avoid cutting up steel-belted portions, and at the same time, to find a way to dispose of several hundred million steel-belted radial tires each year.
I have not only found a way to do this, but have serendipitously provided a highly useful article which lends itself to being tailored for a multiplicity of mundane but nevertheless essential purposes.